Integrated circuits are attached to external circuits with interconnects. The most widely used interconnect is the wire bond. Single or multiple wire bonds connect the bond pads on the integrated circuit to external network terminals which are typically package pins or printed circuit traces. One disadvantage of wire bonds is the parasitic inductance associated with long bond wires. The parasitic inductance introduced by wire bonds is especially problematic in high frequency applications. Another disadvantage to wire bonds is the variability of the wire length and position relative to the circuits and ground planes, and the variability in positioning the chip with respect to the external circuit.
One method of reducing interconnect inductance and variability is to use ribbon or mesh instead of wire bonds. However, parasitic inductance is still an issue, and there are additional equipment and assembly costs associated with ribbon bonders. Furthermore, mesh bonds typically require expensive hand assembly.
Another type of interconnect used to reduce inductance is a beam lead. Connecting integrated circuits with beam leads is effective in reducing inductance, but hand assembly is typically required, and beam leaded integrated circuits require special processing and handing. Extra die area is required for beam leads, which increases circuit costs. Furthermore, beam lead attachment is not compatible with a standard low-cost package. In addition, since the circuit is attached through the beams, the thermal resistance of the attachment is high compared to conventional epoxy or solder attach of the backside of the chip to a package floor.
Flip-chip die attachment solves many of the problems associated with bonds, ribbon or mesh and beam leads. Parasitic inductance is very low and die placement can be very precise with automated equipment. However, a significant disadvantage is the high thermal resistance. Heat flows from the circuit to the package or ground through a limited number of attachment pads, making flip-chips unsuitable for circuits such as power amplifiers which require good heat sinking. Also, since the circuit is upside down after attachment, the circuit is not accessible, which may be a disadvantage for some applications.
Note that the drawings in the figures are not to scale.